The invention relates to a cross member unit for universal joints. The cross member unit has a cross member with four arms. Each two arms define a common longitudinal axis and each arm has an end face. A cylindrical bearing face adjoins the end face which, in turn, is followed by a sealing face and furthermore a seat portion. A bearing bush is provided per arm. The bearing bush includes a tubular, cylindrical casing whose inner face is designed as a running face. The bearing bush is arranged coaxially around the arm with an annular gap. The bearing bush has a base which covers the arm end face and the bearing bush open end includes a running face. Rolling contact members, in the form of rollers or needles, are rollingly arranged in the annular gap. The rollers or needles form a ring around the arm on the running face of the arm and on the inner face of the casing. An annular main seal is firmly inserted into the bearing bush from the open end. The seal includes at least one sealing lip to seal the sealing face of the arm. An annular preseal is arranged on the seat portion of the arm. The preseal includes a sealing lip to sealingly rest against the running face provided at the open end of the bearing bush.
A cross member unit is described in EP 03 21 076. Here, the main seal is fixed to the inner face of the bearing bush by means of a metallic carrier. The seal has two sealing lips. One lip sealingly rests against a cylindrical sealing face of the cross member arm. The other lip rests against a conically extending sealing face of the cross member arm. Furthermore, a preseal is provided in the form of an angle ring arranged on a cylindrical face of the arm. The cylindrical face adjoins the sealing face for the sealing lips of the main seal. The preseal extends over the outer face of the bearing bush by means of a leg which extends parallel to the inner face of the bearing bush. Together with an inwardly directed bead engaging a groove in the outer face of the bearing bush, the preseal forms a labyrinth seal. Friction contact does not exist between the bearing bush and the preseal. However, the preseal itself is positioned, through friction contact, on the associated seat portion of the arm of the cross member.
An improved embodiment of such sealing assemblies with a main seal and preseal for relubricatable cross member units is described in DE 88 05 833 U1. Here, the main seal is firmly inserted into the bearing bush and is provided with two sealing lips. The lips seal a cylindrical sealing face of the cross member. The preseal is arranged, via an annular portion, on a cylindrical portion of the cross member. The cylindrical portion constitutes an extension of the sealing face for the sealing lips of the main seal. The preseal is supported on a curved face, if viewed in the axial direction of the arm. Furthermore, starting from said first leg used for fixing the preseal on the arm, the preseal includes a second leg which is arranged at a radial distance, with reference to the longitudinal axis, and is connected to the first leg by a web. Also, the second leg externally extends over the bearing bush.
All the above embodiments are disadvantageous in that there is no defined seat for the preseal on the cross member arm. Thus, there may be an increase in wear and leakages may also occur. The preseal is able to rotate on the arm, which means that the preseal fit progressively loosens. It is possible for lubricant to leak out and if the seal moves on the seat face, it may be destroyed.
In the case of commercial vehicles, especially high performance vehicles, the objective is to reduce maintenance periods to a minimum. If possible, it is desirable to guarantee a predetermined maintenance-free service life. The service life, in the case of commercial vehicles, is approximately 1 million kilometers. In particular, this applies to vehicles with a permitted gross vehicle weight of more than fifteen (15) tons.